Drawn steel cartridge case and its manufacture



H. F. HILD Sept. 22, 1959 DRAWN STEEL CARTRIDGE CASE AND ITS MANUFACTUREFiled Sept. 12, 1956 3 Sheets-Sheet l INVENTOR. HENRY F. HILD BY %O%Adug 4/14 M ATTORNEYS! Sept. 22, 1959 H. F. HILD 2,904,873

DRAWN STEEL CARTRIDGE CASE AND ITS MANUFACTURE Filed Sept. 12, l956 3Sheets-Sheet 2 xam INVENTOR.

HENRY E HI LD ATTORNEYS:

Sept. 22, 1959 H. F. HlLD 2,904,873

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BY w z. Jam/m #J 2 ATTORNEYS DRAWN STEEL CARTRIDGE CASE AND ITSMANUFACTURE Henry F. Hild, Merion Station, Pa., assignor to the UnitedStates of America as represented by the Secretary of the ArmyApplication September 12, 1956, Serial No. 610,047

Claims. (Cl. 29-13) This invention relates to a drawn steel cartridgecase and its process of manufacture and has for an object to provide acartridge case of steel which is adapted to be extracted from a gunafter firing, without danger of rupture of the base flange engaged by anextractor especially at low temperatures. Another object is to provide amethod of manufacture for such a cartridge case.

The most common type of cartridge case has been of brass because of itsability to be Worked and because brass seems to retain its ductilitythroughout the fabrication of such a case. For well over three decadesthere has been a need for a steel cartridge case due to the possibilityof the supply of the components of brass being stopped when largely fromout of this country, and the realization that in time of nationalemergency steel would be available where brass might not be plentiful.In the face of that old need no satisfactory steel cartridge case hasbeen developed probably due to the fact that no satisfactory way ofmanufacturing it has been devised. The present invention fills that oldneed better than have any of the many prior art attempts. One evidenceof this fact is found in ability of the extractor flange on the base ofthis steel cartridge case to withstand the stress of ex traction afterfiring a 20 mm. cartridge case at an extremely low sub-zero temperaturewithout fracture. On firing, the gas pressure of the explodingpropelling charge swells the steel cartridge case into tight contactwith inner wall of the chamber making extraction of the case difficult.With the development of higher gas pressures in antiaircraft ammunitionthe problem became still more difficult. A common way that a steelcartridge case of the prior art failed was by rupture of the base flangeengaged by the extractor.

It is known that when almost any cartridge case of steel after beingcold worked is longitudinally cut in halves and the cut face etched andpolished, that the flow lines revealed therein indicate the strength orweakness of the metal and the direction under which fracture may occur.Rupture under shear or flexure in a base flange would 'be likely tooccur along or longitudinally of the flow lines. In drawn metal cases itis not feasible to have the flow lines all parallel to the oppositefaces in the base flange and also parallel to the curvature of theextractor groove.

According to this invention the base flange is made under conditions offree and unimpeded yet directed or controlled radial outward flow ofmetal to minimize the danger of the flow lines not being in the rightdirection. The flow lines in the flange being formed have U-shaped bendsin a radial outer portion, such bends connecting generally parallellines about equally distant from each face. Each such U bend is theradial outer terminus of almost each flow line. It is appreciated thateach U bend in the flow lines has too large a part of its length at anangle to the opposite faces of the flange to make the flange as strongas it should be. Therefore, to enhance the flange strength, the radialoutward guided but free flow of metal has been continued until a majorportion l atented Sept. 22, 1959 of all such U bends in the flow linesare radially outside the diameter of the cartridge case walls, thusleaving a majority of the flow lines within that diameter parallel tothe opposite faces of the base and conforming to the curvature of thegroove. To remove the weakness, the outer part of the flange containinga majority of such U bends has been cut off and scrapped. While a smallminor part of the former total number of horizontally disposed U bendsremain, they are not on an outer surface of the flange so that theinherent weakness in U bends in the flow lines is located in atransverse mid-portion of the flange where fiber stresses in flexure aresmaller than on the flange faces, unlike the prior art.

Features in the process of forming the stronger steel cold workedcartridge case of this invention include not only the controlled freeradial outward flow of base material and the cutting ofi of most of theweak U bends, but also a preliminary free flow of metal longitudinallyfor a twofold purpose. One of those is to have the flow lines in aposition ready for the radial outward free flow of metal. The second isto have this longitudinally flowed metal in position for strengtheningprimer pocket.

Fig. 1 shows the work after it has been preliminarily cupped and drawn.

Fig. 2 shows the work after it has been preheaded.

Fig. 3 shows the work at substantially the conclusion of the headingoperation.

Fig. 4 shows the work at the end of the heading operation after it hasbeen removed from the tools and die in which formed.

Fig. 5 is an enlarged longitudinal section of a lower portion of thecartridge case before the outer part of the flange is cut off.

Fig. 6 is a view of the base end of the finished cartridge case partlyin section after the flange has been partly cut off.

Fig. 7 is an enlarged view of the prehead in longitudinal section afterthe section has been polished and etched to show the flow linestructure.

Fig. 8 is an enlarged view corresponding to Fig. 5, showing the generalflow line structure as it was believed to be about four years ago.

Fig. 9 is a view corresponding to Fig. 8 after an outer portion of thebase flange has been cut off.

Figs. 10 to 13 show successive steps in formation of the head from theprehead and show in greater detail the approximate flow line structureat each step.

To form the drawn cartridge case of this invention a disc of SAE 1030steel known as MILS 3289 containing .25 to .35 carbon is cupped anddrawn in a manner wellknown to those skilled in this art, to form thehollow cylindrical body 3 having a thick base 5 closing one end as shownin Fig. 1. After the cupping operation the work is annealed and it islikewise annealed after each of the first and second drawing operations,but no more annealing takes place later. After the second drawingoperation and annealing, the open end of the cartridge case is trimmed,after which it is subjected to a third and fourth drawing to lengthenthe same. There is then a second trimming operation. These operationsneed not be illustrated or described since they are well-known in theart.

A preheading operation is performed as shown in Fig. 2 with the head ofa stationary anvil 7 snugly fitting within the hollow body 3, which issurrounded by a die or matrix 9, a movable punch 11 engages the oppositeside of the base from that on which the hollow body was formed, suchpunch moving into the base causes the metal of the base to be coldflowed longitudinally. The

walls 15 of the cylindrical cavity 13 in the die 9 preclude the metalbulging radially outwardly. In the die 9 is shown a cavity 16 of reduceddiameter so that as the metal is flowed longitudinally it is guidedinits free flow by the upper end of the punch 11 in the walls 16 of thecavity. The tip 19 of the punch 11' is rounded to facilitate the flow ofmetal and it is importantthat a space 2]. always remain at the extremityof the annulus or prehead 23 to insure the longitudinal flow of metalbeing as free as is possible without any compacting of the metal orcongestion of the flow lines 25, 27, 29 and 31. This is shown in Fig. 7.There may be additional flow lines in the spaces 28 and 3t) of thepreheaded case 33 as shown in Figs. 7 to 9.

In Fig. 3 during the heading operation illustrated, another anvil 35 isinserted within the cartridge case surrounded by the die 37. At the endof the prehead a pair of semicircular jaws 39 engage the work toconstitute a sizing ring. The curved walls 41 of these jaws are providedwith the chamfer 43 to engage the corresponding bevel shown in Fig. 2for the purpose of preventing any distortion of the work in the portionengaged between said semicircular jaws 39. For engaging the longitudinalend of the prehead, there is providing a sizing punch 45 having aninsert 47 which latter limits the radial inward flow of metal in theforrnation of the primer pocket 67 shown in Figs. 6 to 9. At theconclusion of the heading operation shown in Fig. 3 a flange 49 isformed.

T he semicircular jaws 39 when removed from the finished product resultin a groove 51 having been formed just above the base flange 49 as shownin Fig.' 4 in which this flange 49 is larger than is desired. Theenlarged longitudinal section shown in Figs. and 8 is that within therectangle A in Fig. 4. The reference numeral 53 designates theunfinished cartridge case. The outer end portion 55 of flange 49 islater cut ofl along the broken line 57 to form the finished cartridgecase 59 as shown in Figs. 6 and 8. This finished product has the usualpropellent chamber 63 and is provided with a flange or head 65 radiallywithin which is a primer pocket 67, with the wall 69 between the primerpocket 67 and propellent chamber 63 having been pierced as illustrated.

A reason for cutting off the radially outer end portion of the baseflange is shown in Fig. 9. It is known that a maximum resistance toflexure and shear is offered where the flow lines in the flange 65 arenormal to the applied force in extraction and parallel to the groovecurvature or in other words when the flow lines are substantiallyparallel to the curvature in the base of the groove and to the forwardand rearward faces of the base flange. The metal of the base would beweakest were the flow lines to extend longitudinally of the cartridgecase. In the outer out 01f portion of the flange the flow lines have aportion extending longitudinally, that is at the tip of the U-shapedbendsin these flow lines. The curved portions of the flow lines eachside of the centers of the U bends are weaker in shear and flexure thanthe portion of the base flange remaining. This is why it is necessary tocut off the radially outer part of the base flange. While it is truethere may be additional flow lines within the spaces 28 and 30, any Ubends in these inner flow lines beingmidway between the flange faces areprotected by a strong metal portion adjacent the forward and rearsurface of the flange. The former Figs. 8 and 9 exemplify the reason forcutting off the outer portion 55 but are not nearly as accurate inportrayal of flow line congestion around the primer part 67, as is theshowing in Figs. to 13.

Referring to the newly added Figs. 10 to 13 it will be seen that in Fig.10 with the sizing jaws 39 in position, the anvil 35 within thepreheaded case 33, the die 57 surrounds the work as shown in Fig. 3 butthis die is not shownin Figs. 10 to 13 for the purpose of clarity. Fig.10 thus shows the beginning of the heading operation after formationofthe preheadshown in Fig. 2. when the sizing punch 45 with its insert 47is moved into engagement with the outer end portion of the prehead orannulus 23 causing the metal in this annulus to be compressed and causea bulge radially both inwardly and outwardly. In Fig. 11 the inwardbulge has been impeded by the end of insert 47 acting as an abutment tolimit radial inward flow of metal. However, radial outward flow of metalas shown at the bulge 70 is free and not impeded. The result is that theabutment 47 causes the flow lines adjacent to it to be compacted ormoved closer together as shown at, 7.1 as the prehead is upset. In Fig.12 the insert 47 continues to act as an abutment causing the flow linesadjacent to it to be moved still closer together while the radialoutward bulge is much more pronounced with the flow lines following thepattern illustrated. The edge 72 on the sizing punch 45 and the edge 73on the sizing ring 39 together cooperate to constitute a constrictionthrough which, themetal freely ,fiows radially outward. Fig. 12 alsoshows how the radial outward ,flowof metal .is not impeded by any radialouter wall. Fig. ,13correspouds to Figs. 10 to. 12 but with theheadingoperation having reached its termination. This figure ,of the drawings.shows how the flow lines have been moved together from the metal havingbeen compacted around the primer pocket making it stiffer and strongerto resist gas pressure 011 firing. It will be seen from Fig. .13 how the.adjacent guide surface 74 comes into full frictional contact with themetal only just beforethe completion of the heading operation. The outerpart of theflange is cut off along the broken line 57 as previouslymentioned in Fig. 5.

Among the advantages of the presentinvention maybe mentioned first theproviding of a stronger than usual base flange due to the absence of Ubends in the flow lines and the presence of compacting of metal aroundthe primer pocket. and the free radial outward flow of metal. Where theradial outer How is not impeded by any radial outer wall, the flow linesadjacent the forward and rearward surfaces of the flange aregeneral-lyparallel tothose surfaces and to the curve in the groove 51 indicatingmaximum resistance to the stress of extraction after removal of theportion 55. Although there may be a horizontal U bend in some remainingportion of the flange flow lines, such weaker portion is protected bythe stronger outer surfaces of the flange faces after a major portion ofthe U bends have been cut off. In Fig. 13 it will be seen the freeradial outward flow of metal is continued until the majority of the Ubends in the flow lines are radially outside the outside diameter of thecartridge case walls. Another advantage of the present invention notshown in Figs. 8 and 9 but better presented in Figs. 10 to 13 inclusive,is'the compacting ofthe metal and flow lines to strengthen the metal inthe side walls of the primer pocket. 'The radial outward fiow of metalin Fig. 12, encounters more frictional contact with the face 75 of thepunch 45 than with the face 74 of the jaws 39. This results in slightlymore compacting of the metal against face 75 than against face 74.

The process of this invention, so far as is known, is useful only forproduction of the product herein claimed, and the product of thisinvention is capable of being made in no other way than by the hereinprocess, so far as is known. v

This application is a c'ontinuation-in-part of prior application SerialNumber 301,823 filed July 31, 1952, now abandoned, for PlasticallyFormed Head for a Cartridge Case.

.I claim:

1. ,In the process of forming a steel cartridge case comprising cuppingand drawing a disc into a hollow cylinder having sidewalls and a closedbase, said disc-initially having grain flow lines parallel to said discsfaces thereby resulting in continuous and unbroken grain'flow lines insaid base and sidewalls, the steps of: flowing the metal of said base ina longitudinal direction away from said sidewalls free of contact withany'end abutment to form a prehead section, the grain flow lines in saidprehead section being continuous and unbroken and forming longitudinallyinwardly facing U bends at the extremity of said prehead section;forming a peripheral outer flange by extruding said prehead sectionradially outwardly under controlled flow free of contact with any radialend abutment; continuing said extruding until substantially all of saidU-bends are outside a finished diameter of said flange; then cuttingsaid flange to finished diameter thereby removing substantially all ofsaid inwardly facing U bends.

2. A process according to claim 1 in which said radial outward flow ofmetal from said prehead section is through a constriction, thensuccessively reducing the size of said constricted portion with outwardflow of metal.

3. A process according to claim 2 which includes clamping said casecircumferentially on said prehead section adjacent said constriction,then guiding the metal extruded through said constriction by radialguides on each side of the extruded metal but not in contact with one ofsaid guides substantially before that metal has reached its desiredradial outer diameter.

4. In the process of forming a steel cartridge case comprising cuppingand drawing a disc into a hollow cylinder having sidewalls and a closedbase, said disc initially having grain flow lines parallel to said discsfaces thereby resulting in continuous and unbroken flow lines in saidbase and sidewalls, the combination therewith of the steps for forming aperipheral outer flange and a primer pocket having increased strength,said steps including: flowing the metal of said base in a longitudinaldirection away from said sidewalls, free of contact with any endabutment, to form a prehead section, the grain flow lines in saidprehead section being continuous and unbroken and forming inwardlypointing U-bends at the extremity of said prehead section; compressingsaid prehead section to press an inner wall against an abutment to formsaid primer pocket while simultaneously: bulging an outer wall of saidprehead section radially outwardly free of contact with any abutment onsaid outer wall radial outer edge, further compressing said preheadsection and forming said peripheral outer flange by flowing metal fromsaid prehead section radially outwardly through a successively narrowingconstriction free of contact with any radial end abutment until a majorportion of said U- bends are radially outside a finished diameter ofsaid peripheral outer flange; then cutting said flange to finisheddiameter, thereby removing a major portion of said inwardly pointingU-bends.

5. A process according to claim 4 which includes clamping said casecircumferentially on said prehead section adjacent said constriction,then guiding the metal extruded through said constriction by radialguides on each side of the extruded metal, said extruded metal beingfree of contact with one of said guides substantially before that metalhas reached its desired radial outer diameter.

References Cited in the file of this patent UNITED STATES PATENTS2,736,085 Parre et al Feb. 28, 1956 FOREIGN PATENTS 128,271 GreatBritain June 26, 1919 719,783 Germany Apr. 16, 1932 732,984 Germany Mar.17, 1943

